This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-012698 filed Jan. 22, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a rotary anode type X-ray tube apparatus, and more particularly to a rotary anode type X-ray tube apparatus having a cooling structure, which can improve a cooling efficiency of a rotary anode type X-ray tube received in a housing.
2. Description of the Related Art
In a rotary anode type X-ray tube apparatus, a rotary anode type X-ray tube is received in a housing, and the rotary anode type X-ray tube comprises a cathode for generating an electron beam, an anode target for emitting X-rays upon irradiation of the electron beam, a rotating mechanism for rotatably supporting the anode target, and a vacuum envelope for enclosing the cathode, the anode target, and the rotating mechanism.
FIG. 1 shows a conventional rotary anode type X-ray tube apparatus. In FIG. 1, numeral 41 denotes a housing, and a rotary anode type X-ray tube is enclosed in the housing 41. A coolant such as insulating oil is filled in a space between the housing and the rotary anode type X-ray tube.
In the rotary anode type X-ray tube 41 shown in FIG. 1, there are enclosed a cathode 44 for generating an electron beam, an anode target 45 for emitting X-rays upon irradiation of the electron beam, a rotating mechanism 46 for rotatably supporting the anode target 45. The rotating mechanism 46 comprises a rotary cylinder 47 to which the anode target 45 is fixed, a stationary shaft 48 for rotatably supporting the rotary cylinder 47, and dynamic pressure type bearings.
In the dynamic pressure type bearings, helical grooves of herringbone patterns are formed on the surface or surfaces of the stationary shaft 48 and/or the rotational structure 47, and a liquid metal lubricant such as gallium or gallium alloy is applied to the helical grooves and a gap space between the stationary shaft 48 and the rotational structure 47. A stator coil 49 for generating a rotating magnetic field is provided outside the vacuum envelope 43 and disposed around the rotary cylinder 47.
A cooler device 50 is located outside of the housing 41 and comprises a heat exchange unit, a pump unit and so on. A coolant outlet path such as an outlet pipe P0 couples the cooler device 50 to the housing 41 to supply a coolant from the cooler device 50 to the housing, and a coolant inlet pipe such as an inlet pipe Pi also couples the housing 41 to the cooler device 50 to return the coolant from the housing 41 to the cooler device 50.
In the apparatus shown in FIG. 1, the insulating oil as the coolant which is heated by the rotary anode type X-ray tube 42 is supplied from the housing 41 to the cooler device 50 via the outlet pipe P0 and the insulating oil which has been cooled in the cooler device 50 is also supplied to housing 41 from the cooler device 50 via the inlet pipe Pi so that the insulating oil is circulated in a circulating path as shown by arrow Y.
In an operating mode, the stator coils 49 applies the rotating magnetic field to the rotary cylinder 47 of the rotating mechanism 46 to rotate the rotary cylinder 47 so that the anode target 45 is rotated. The electron beam generated from the cathode 44 is accelerated by a high voltage between the cathode 44 and the anode target 45 and is impinged on the rotated anode target 45 so that X-rays are emitted from the rotated anode target 45. The X-rays pass through a radiation window W1 provided on the vacuum envelope 43 and a radiation window W2 provided on the housing 41 and are guided outside of the housing 41.
Heat is generated from the anode target 45, stator coils 49, the dynamic pressure type slide bearing between the stationary shaft 48 and the rotary cylinder 47, and so on, and is transmitted to the insulating oil circulated between the cooler device 50 and the housing 41. Thus, the insulating oil absorbing the heat cools the X-ray tube.
The dynamic pressure type bearing has advantages of low noise, low vibrations, and long life due to small rotational friction. However, a shearing force is applied to the liquid metal lubricant in rotation of the rotary cylinder and a shearing energy is transferred to the liquid metal lubricant so that the liquid metal lubricant is heated due to the shearing energy and a temperature of the dynamic pressure type bearing is increased. Thus, a diffusion reaction is prompted between the liquid metal lubricant and a bearing material of the rotary cylinder and the stationary shaft. As a result, it may be impossible to constantly maintain a stable rotation of the rotary cylinder. Accordingly, a method of cooling the bearing is employed in the conventional X-ray apparatus, in which a coolant space is provide in the stationary shaft constituting the rotating structure and the insulating oil is supplied to the coolant space to cool the bearing section of the stationary shaft.
There will be described a conventional rotary anode type X-ray tube apparatus having a stationary shaft of a bearing with reference to FIG. 2, in which a coolant space is formed. In FIG. 2, same numerals denote same parts or members in FIG. 1, and a detailed description thereof will be omitted.
A hollow space 51 for circulating a coolant such as an insulating oil to cool a stationary shaft 48 is formed in the stationary shaft 48 in an axial direction and a pipe 52 is so arranged to extend in the hollow space 51 in the axial direction. The pipe 52 is coupled to the inlet pipe Pi at a bottom end 52A thereof and is extended along the hollow space 51, and a top end 52B of the pipe Pi is closely faced to the inner bottom of the pipe Pi.
In the configuration shown in FIG. 2, the insulating oil passing through the inlet pipe Pi is guided in the pipe 51 and flows in the pipe 51 as shown by arrow Y1. The insulating oil is supplied from the opening of the top end 52B to the flow space and path between the pipe 51 and the stationary shaft 52. Then, the insulating oil flows in the flow path and outlets in the space of the housing 41, as shown in FIG. 2. The inlet pipe Pi, the pipe 51, and the flow path between the pipe 51 and the stationary shaft 52 constitutes a part of the circulating coolant path for guiding the insulating oil, which cools the bearing to maintain the temperature of the bearing in a predetermine temperature range.
Thereafter, the insulating oil flowed from the flow path in the stationary shaft 52 into the space in the housing 41 flows to the stator coils 49 and the vacuum envelope 43 to absorb heat generated from the stator coils 49 and the vacuum envelope 43 and is supplied to the cooler device 50 through the outlet pipe P0.
In the conventional rotary anode type X-ray tube apparatus, the coolant hollow space is provided in the stationary shaft constituting the rotating mechanism to absorb heat generated from the bearing, and so on. In this construction, an inner diameter of the stationary shaft in the coolant hollow space can not be set to be relatively large, because the stationary shaft has a relatively small outer diameter and the stationary shaft must have a sufficient mechanical strength. If the stationary shaft has a small inner diameter to have a sufficient mechanical strength, a pressure loss is produced in the coolant flow space or path in the stationary shaft, and a flow rate of the coolant circulating in the apparatus is lowered and the circulating amount of the coolant is decreased in the apparatus. Thus, a cooling efficiency of cooling the stator coils, the vacuum envelop and so on is lowered due to the lowering of the circulating amount of the coolant.
There is an improved method of increasing a cooling efficiency, in which a pumping ability of pumping the coolant is increased in the cooling device. To increase the pumping ability, it is required to design the device to have a large size. Thus, the cooling device becomes high in cost. Although, if the pumping ability is increased, the cooling efficiency may be set to a high level and a viscosity may be large due to the excessive cooling of the bearing and the liquid metal lubricant, and lowering the temperature of the liquid metal lubricant to an unexpected one. Thus, a rotation torque may become unsuitably large within a range of a rotation rate required for the anode target, thus requiring more power to be supplied to the stator coils.
An object of the present invention is to provide a rotary anode type X-ray tube apparatus which can effectively absorb heat generated from a bearing without lowering an amount of coolant flowing through a housing of the apparatus.
According to the invention, there is provided an X-ray tube apparatus comprising:
an X-ray tube including;
a rotary anode target;
a cathode configured to generate electrons to the anode target to cause the anode target to emit X-rays;
a rotary cylinder coupled to the anode target:
a stationary shaft configured to rotatably support the rotary cylinder, the stationary shaft having an opening and a hollow space communicating with the opening;
a dynamic pressure type bearing provided between the stationary shaft and the rotary cylinder; and
a vacuum envelope configured to receive the anode target, the stationary shaft, the rotary cylinder, and the bearing;
a housing configured to receive the X-ray tube, in which a coolant is filled;
a cooler device configured to cool the coolant and circulate the coolant between the cooler device and the housing:
a coolant splitter configured to split the coolant supplied from the cooler device into coolant streams in the housing, one of the coolant streams being guided in the hollow space of the stationary shaft.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.